A known piston bearing structure for a fluid pressure cylinder is such that a piston is supported in a cylinder tube via one seal ring and two wear rings sandwiching this seal ring.
As the seal ring of this type, JP2010-14201A and JP2008-138805A disclose a seal ring including two pairs of lips projecting to the inner and outer peripheries thereof and having an X-shaped cross-sectional shape.
On the other hand, the wear rings of this type fulfill a backup function of supporting the seal ring so that the lips does not protrude from a housing groove and a bearing function of slidably supporting the piston relative to the cylinder tube.
Further, a pressure difference between the piston and the cylinder tube and between opposite sides of the wear rings is suppressed by defining clearances around the wear rings, thereby preventing the wear rings from being deformed due to the pressure difference when the fluid pressure cylinder extends and contracts.